Apparatus for incandescent filament mounting

ABSTRACT

Automotive vehicle equipped with incandescent lamp filament mounting which isolates the filament from vibrations at the resonant frequency of the filament, thereby extending the life of the filament. The frequency isolation is accomplished with an exponential spring. The spring is secured to a lamp body and a socket is mounted at the node of frequencies which are the resonant frequency of the filament.

United States Patent 1151 3,678,266 Fradette [451 *July 18, 1972APPARATUS FOR INCANDESCENT [56] References Cited FILAMENT MOUNTINGUNITED sTATEs PATENTS [72] Inventor: Joseph J. Fradette, Cleveland, Ohio209,678 11/1878 1,020,062 3/ 1912 [73] Assignee. White Motor CorporationI 2,051,324 8,1936 Notice: The portion of the term of this patent sub- J1933 sequent to Dec. 16, 1986, has been dis- 313271110 6/1967 FOREIGNPATENTS OR APPLICATIONS [22] 1969 573,277 6/1924 France ..240/90 [21]Appl. No.: 878,690

Primary Examiner-Richard C. Queisser Related US. Application DataAssistant Examiner-Herbert Goldstein [62] Division Of Ser. NO. 639,124,May 17, 1967, Pat. NO. 3,484,600. [57] ABSTRACT [52] U.S.Cl...240/90,240/8.2,240/8.3, Automotive vehicle equipped with incandescentlamp fila- 313 2 9 ment mounting which isolates the filament fromvibrations at 51 Int. Cl. ..F2lv 15 04 the resonant frequency of thefilament, thereby extending the 58 Field 61 Search ..240/7.1 8.2 8.3 90-life the filament The frequency islatin is P with an exponential spring.The spring is secured to a lamp body and a socket is mounted at the nodeof frequencies which are the resonant frequency of the filament.

5 Claims, 6 Drawing Figures PATENTED JUU 8 I972 SHEET 1 BF 2 mm I mm.THHMWX E? m i\ V M 6 w M m @w amma; I i

B M g ATTORNEYS PAIENTEU JUL] 8 I972 SHEET 2 [IF 2 INVENTOR. JOSEPH J.FRADETTE %%rwf ATTORNEYS APPARATUS FOR INCANDESCENI FILAMEN'I MOUNTINGThis is a division of US. Pat. application Ser. No. 639,124, filed May17, 1967 and now U. S. Pat. No. 3,484,600.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention isdirected to a filament mounting for incandescent lamps and primarilydirected to a mounting for the socket of small automotive lamps. Themounting is in the form of a spring which isolates the filament fromvibrations at the resonant frequency of the filament.

In the automotive industry, the advent of 12-volt systems aggravated aproblem that, prior to this discover, had. never been satisfactorilysolved. The problem is that of excessive filament failure. The increasedfailure, as compared with 6- volt systems, is due to thesmaller-filament sizes in l2-volt bulbs of corresponding candle power.The filament breakage in fact is such a problem that, in heavy-dutydiesel trucks and the'like, it has deterred the truck manufacturingindustry from changing to 24-volt systems. A 24-volt system is desirableand, in the view of some, essential in order to obtain adequate crankingpower in the starting systems for heavy-duty diesel engines.

In attempting to detemiine the cause of filament failures, I conducted asurvey of small bulbs such as those used in truck marker and stop lamps.In analyzing a relatively large number of such bulbs after theirfilaments had failed, I determined that over 90 percent of the failuresare what can be termed cold failures. That is, over 90 percent of thebulbs failed at a time when they were not illuminated and hot. Theexplanation for this is that the vast majority of lamp failures in thepast have been caused by vibrations and the filaments are more brittlewhen cold than when hot.

A typical highway tractor will be equipped with five socalled markerlamps. It is fair to say that the average life of those lamps has beenapproximately 5,000 miles. Most such bulbs, so far as my survey coulddetermine, failed due to breakage of the filament caused by vibrationand very few burned out. Most such lamps which burned out were lampsfrom instrument panels within the cab where vibrations are minimized.

By contrast, in tests conducted with lamp assemblies made in accordancewith this invention, all bulb failures have been due to burn out of thefilament. The earliest bulb failure that has yet been experienced was at155,000 miles and the second earliest was at 181,000 miles. In onetruck, of five marker lamps, two were still operating at 423,000 milesand the other three had burned out at various times after the truck hadtraveled in excess of 400,000 miles.

Thus, the fact that one bulb failed at 155,000 miles by buming outsimply suggests that that bulb was not as well constructed as thosewhich have lasted in excess of four hundred thousand miles. What haspreviously been substantially, if not universally, the cause of failurebreakage due to vibrationhas been substantially completely, if notcompletely, obviated.

2. The Prior Art Previously, it has not been recognized that excessivefilament failure has been caused by vibrations at the resonant frequencyof the filament and that the filament can be isolated from suchvibrations. While there have been proposals for lamp constructions inthe past where a socket is spring mounted to isolate the lamp fromshock, none have been expressly designed to dampen vibrations equal toor in beat with the natural frequency of a filament. The result has beenexcessive filament failure.

SUMNIARY OF THE INVENTION Tests were conducted with a selected bulb typein an attempt to determine the cause of bulb failure. A fatigue curvewas generated forthe selected bulb type which showed the criticalfrequency to be 1125 cycles per second. At such a frequency on vibrationtests, filaments would break in a very short period of time.

It was then discovered that if the socket was mounted at a particularlocation on the spring, the filament would be completely free ofvibration when the resonant frequency of the bulb, 1,125 cycles persecond in this example, was applied to the base of the spring. Thus, thesocket is mounted at the node for the resonant frequency of the filamentof the bulb to be used, totally isolating the filament from its nautralfrequency. The isolation of the resonant frequency in this test examplewas so successfirl it was possible to use smaller bulbs requiring lessthan fifty percent the amperage because the mechanical strength of thelarger filament was no longer required to inhibit filament breakage.

It is believed that in any vehicle operating along a road, it can beassumed that there are random vibrations imposed on each lamp typicallyand therefore periodically. By appropriate positioning of the filamenton a selected spring, this periodic vibration at the resonant frequencyof the filament cannot introduce any work energy into the system. Thiseffectively filters out the resonant frequency so that the filament isnever excited or forced to vibrate at its resonant frequency.

It has also been discovered that certain spring shapes are advantageousin designing a filament support which will isolate resonant frequencies.It has been discovered for example that if a spring which is tapered inits transverse dimension is used, the positioning of the socket andtherefore of the filament along the spring is far less critical than itis with a spring which is rectangular or trapezoidal in shape. It hasfurther been discovered that the best results are obtained if theconfiguration of the sides of the spring is exponential. For reasonsthat are not fully understood, this results in a range of points alongthe narrower end of the spring where the filament is isolated from itsresonant frequency.

In the situation where, as in a tail lamp, there are two filaments,normally one is a minor and the other a major filament. That is, in thetail lamp example, the tail light filament will be relatively small andthe stop light, being of considerably more candle power, is relativelylarge and heavy. In that circumstance, the lamp assembly is constructedto isolate the minor filament from vibrations since it is the minorfilament which most frequently fails first due to vibrations.

. It will be appreciated that while in the summary the description hasbeen directed to a construction where the socket is mounted on a spring,it is within the scope of the invention to, in larger bulbs such assealed-beam headlights for example, mount the filament itself on a pairof springs which serve as the conductors for supplying electric energyto the filament and also serve to isolate the filament from vibrationsof its own resonant frequency.

The construction of this assembly then has the advantages of very markedimprovement in the life of the filaments. This permits 24-volt, or evenhigher volt systems where desired, and even isolates the lamp fromshock. It also permits the use of smaller lamps with lower currentdrains in many applications where, prior to this invention, bulbs oflarger size than required for the lighting function were used simply toprovide filaments having sufficient mechanical strength to lastsomething resembling a reasonable length of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of ahighway tractor equipped with lamp assemblies of this invention;

FIG. 2 is a cross-sectional view of an improved marker lamp assembly;

FIG. 3 is a top plan view of the base and socket and supportingstructure of the lamp assembly of FIG. 2;

FIG. 4 is a plan view of the filament resonant frequency isolatingspring of the assembly of FIGS. 2 and 3 prior to bending into itsfinished configuration;

FIG. 5 is a somewhat diagrammatic view illustrating the flexure of afrequency isolating spring of a lamp assembly made in accordance withthis invention; and,

FIG. 6 is a somewhat diagrammatic sectional view of a sealed-beam lampwith frequency isolating springs within a glass envelope and directlysupporting a filament.

Referring to the drawings and FIG. 1 in particular, a highway tractor isshown generally at 10. The tractor has the usual road wheels 1 l and isof the wellknown cab-over-engine type. The tractor has a cab 12 mountedabove an engine (not shown) and the road wheels. The illustrated tractorhas five marker lamps l3 and sealed-beam headlamps 14.

Referring now to FIGS. 2 and 3, the marker lamp assembly includes asomewhat dome-shaped lens 16. The lens is of conventional molded plasticconstruction with flutes, not shown, along sidewall portions 17. Thelens 16 has a pair of mounting tongues 18 which, when the lamp isassembled are below mounting flanges 20 of a mounting ring 21. Theflanges 20 project into a groove 23 in the lens and above the tongues18.

The tongue and mounting ring construction is more clearly understood byreference to FIG. 3 and is conventional. The mounting ring 21 is securedto a base 25. The mounting ring 21 has a pair of diametrically opposedcut-out portions 24. When the lens 16 is connected to the base 25, thetongues 18 are passed through the cut-out portions 24. The lens is thenpressed inwardly against a deformable sealing gasket 26 and rotateduntil the tongues 18 are disposed beneath the mounting flanges 21.

The base is metal. A base gasket 25A is provided. The gasket 25A ismolded of a suitable material such as soft rubber. The base 25 andgasket 25A include a wire passage 27 for a supply conductor 28. A socketassembly shown generally at 29 is riveted or otherwise suitably securedto the base as by rivets 30, 31 connected to a ground strap 32. Theground strap 32 is suitably grounded to the frame when the base 25 issecured to the frame as by fasteners inserted through the mountingapertures 33, FIG. 3.

The socket assembly 29 includes the usual contact 26 connected to thesupply conductor 28. The contact is biased by a contact spring 37 intoengagement with base 38 of a bulb shown generally at 40. The bulb 40 hasa shank 41 which is conventionally secured to a socket 42. The socket 42serves both to mechanically mount the bulb and to provide a connectionto grounding on the frame. The bulb 40 has the usual generally sphericalglass envelope 44 which houses a filament 45. The filament 45 isconnected by conductors 46 to the base 38 and to the shank 41 in theusual manner.

The socket 42 is connected to the base 25 by a frequency isolationspring 50. The spring 50 is preferably of a construction in which thetransverse dimension diminishes from a base end 51 to a smaller socketmounting end 52, FIG. 4. As indicated in the introduction to thisapplication, the construction is preferably exponential so that sides53, 54 are in the shape of logarithmic curves. It has been found thatwith this exponential construction, location of a conductor aperture 55near the socket end 52 of the frequency isolation spring 50 is far lesscritical than with rectangular or trapezoidal configurations and in factconsiderably less critical than with a linearly tapered construction.

The range of suitable locations for the conductor aperture 55 andtherefore the axis of the socket 42 is indicated in FIG. 4 by the lines56, 57. With rectangular or trapezoidel configuration, the locus ofpoints which will be along a node of the resonant frequency of afilament will be essentially a line transverse to the spring while, asindicated schematically by the lines 56-57 it has been found that thesocket may be positioned with its axis anywhere within the generallyrectangular configuration between those two lines.

It has been further found that in order to provide a satisfactory andstable mounting, space for the wire, and the like, without detractingfrom the characteristics of the mounting on an exponential type spring,the frequency isolation spring 50 may have leg portions 59, 60. Theseleg portions have transverse dimensions which are exponential. In otherwords inner surfaces 61, 62 of the leg portions 59, respectively, are exponential with respect to sides 53, 54 respectively.

It will be recognized from an examination of FIGS. 2 and 3 in comparisonwith FIG. 4 that the spring shown in a flat condition in FIG. 4 is bentat 64 to provide the mounting configuration shown in FIGS. 2 and 3. Itwill be further recognized that the portion of the spring adjacent thesocket end 52 is somewhat enlarged to provide adequate body to thespring for secure mounting of the socket 42. Nonetheless, the spring isexponential in shape and the axis of the socket is secured to theisolation spring 50 at a location where frequencies of a resonant levelof the filament are isolated. The isolation is demonstrated by referenceto FIG. 5. There, the vibrations of the isolation spring 50 areindicated schematically by dotted lines. As shown, the lamp assembly 29remains essentially stationary with respect to the base 25 even thoughthe spring is vibrating appreciably at the frequency which is theresonant frequency of the filament 45.

It has also been found that the conductor 28 may conduct vibrations atthe resonant frequency of the filament 45. Accordingly, the conductoraperture 27 in the base 25 is radially offset from the conductoraperture 55 in the isolation spring 50 to provide bends at 65, 66, inthe conductor, which bends permit the wire to flex and therefore fail totransmit vibrations to the filament.

Referring now to FIG. 6, the sealed-beam headlamp 14 is shown in asomewhat schematic form there. The headlamp 14 has an envelope 70 whichhouses a filament 71. Conductors 72, 73 which support the filament 71are secured at their bases to the remainder of the headlamp. Theconductors 72, 73 are formed to be exponential vibration isolationsprings so that resonant frequencies of the filament 71 are nottransmitted to it. It is preferred that the isolation conductors 72, 73differ somewhat from one another in configuration so that they do notresonate with one another.

The proper location of the socket 42 on the spring 50 is determined bytrial and error. So far as I am aware, there is no mathematical formulafor determining the appropriate and critical distance from the rivets30, 31 to the axis of the socket. One process that has been developed isto:

1. First determine the resonant frequency of the filament;

2. Apply vibrations to the base of the frequency isolation spring at theresonant frequency; and,

3. Trim the length of the spring by trial and error until the filamentdoesnt vibrate at that resonant frequency. A stroboscope may be used forthis purpose.

After the appropriate length has been determined, a die can beconstructed to accurately and inexpensively produce springs of theappropriate length.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. In an incandescent light mounting fixture for a vehicle:

a. a base;

b. a light bulb assembly housing including a filament;

c. a socket assembly supporting said bulb assembly; and,

d. a leaf spring supporting said socket assembly on said base; saidspring comprising:

1. a base end defined by first and second leg portions integrallyconnected to said base;

2. a socket mounting end;

3. a generally U-shaped bend intermediate said ends whereby said socketmounting end is spaced from said base;

4. sides of said spring tapering from near said base end around at leastpart of said bend toward said socket mounting end whereby said spring iswider across said base end than across said socket mounting end; and,

5. said legs merging at a location spaced from said base.

2. In a mounting fixture as claimed in claim 1 wherein said socketmounting end extends substantially parallel to said base.

3. A mounting fixture as claimed in claim 2 wherein said legs mergetogether along said bend.

4. A mounting fixture as claimed in claim 1 wherein said ductor.

' base defines an opening through which an electrical conduc- 5. Amounting as claimed in claim 1 wherein each of said leg tor extends tosaid socket assembly, said conductor loosely ex- PQ defines at least Pof one of Said tapered f tending between said base and said socketassembly whereby 531d Sprmgflexure of said spring is substantiallyunimpeded by said con-

1. In an incandescent light mounting fixture for a vehicle: a. a base;b. a light bulb assembly housing including a filament; c. a socketassembly supporting said bulb assembly; and, d. a leaf spring supportingsaid socket assembly on said base; said spring comprising:
 1. a base enddefined by first and second leg portions integrally connected to saidbase;
 2. a socket mounting end;
 3. a generally U-shaped bendintermediate said ends whereby said socket mounting end is spaced fromsaid base;
 4. sides of said spring tapering from near said base endaround at least part of said bend toward said socket mounting endwhereby said spring is wider across said base end than across saidsocket mounting end; and,
 5. said legs merging at a location spaced fromsaid base.
 2. a socket mounting end;
 2. In a mounting fixture as claimedin claim 1 wherein said socket mounting end extends substantiallyparallel to said base.
 3. A mounting fixture as claimed in claim 2wherein said legs merge together along said bend.
 3. a generallyU-shaped bend intermediate said ends whereby said socket mounting end isspaced from said base;
 4. sides of said spring tapering from near saidbase end around at least part of said bend toward said socket mountingend whereby said spring is wider across said base end than across saidsocket mounting end; and,
 4. A mounting fixture as claimed in claim 1wherein said base defines an opening through which an electricalconductor extends to said socket assembly, said conductor looselyextending between said base and said socket assembly whereby flexure ofsaid spring is substantially unimpeded by said conductor.
 5. A mountingas claimed in claim 1 wherein each of said leg portions defines at leastpart of one of said tapered sides of said spring.
 5. said legs mergingat a location spaced from said base.